This application claims the benefit of Korean Patent Application No. 2000-11705, filed on Mar. 6, 2000.
1. Field of the Invention
The present invention relates to an on screen display system, more particularly to an apparatus and method for simultaneously displaying different image signals using a blending method.
2. Discussion of the Related Art
In a display device, On-Screen Display (OSD) technology is used to process various image signals and display the selected images on a screen. OSD technology is one type of character display techniques that displays various data such as channel number and volume on a TV screen. It displays such data in a character, figure, or graphic format. OSD technology can simultaneously provide a user with displayed image data and other data, such as a caption, and allows the effective use of an image processing system.
It is expected that the OSD method will be further developed in the future in conjunction with the rapid development of related technologies. One example is the ASIC technology used in digital television or display devices. Suppliers of these devices will request, in light of consumer expectations with regards to on screen displays, improved levels of OSD technology.
A Color Look-Up Table (CLUT) of 16 entries is generally used in the OSD. The CLUT is a table that stores color data such as Y, Cb, and Cr, which represents the OSD. In the case where a bit map of 2 bit/pixel is used, the CLUT requires a color map as an intermediate step because it cannot directly use the bit map of 2 bits per pixel as an address of the CLUT. In the case where a bit map of 4 bits per pixel is used, the CLUT does not require a color map because the bit map can be used directly as an input address of the CLUT. In cases where a bit map of greater than 4 bit/pixel is used, the CLUT should have 16 entries or more. Dimensions of the bit map in the OSD are generally within the range of 720xc3x97480 (NTSC mode) or 720xc3x97576 (PAL mode). Also, in the above cases where a bit map is used, the data transmission amounts between an external memory and an OSD controller can be increased if the dimensions of the bit map stored in the external memory are great. However, the data transmission amount is reduced in the OSD image because infrequent occurance of a temporal variance of the OSD image.
For example, since a caption maintains a uniform bit map for one to two seconds, the bit map does not change for 50 to 60 frames. Also, in the case of an OSD screen that displays a menu selection on an initial screen, the OSD bit map is unchanged until a viewer selects one of the menu.
The blending method is one example of the various OSD technologies. The blending method simultaneously displays different images by making the images translucent. The blending method is one of the most important OSD technologies.
In the blending method, a blended image Out1 is displayed by adding a first image signal V1 to a second image signal V2 based upon a blend coefficient (xcex1-coefficient) previously set in a pixel unit. This operation can be expressed as follows:
Out1=xcex1xc3x97V1+(1xe2x88x92xcex1)V2xe2x80x83xe2x80x83(1) 
V1: optional image signal
V2: image signal to be added
xcex1: blend coefficient
In the above formula (1), the blend coefficient xcex1 has a value of 0 less than xcex1 less than 1. As an example, supposing that xcex1=0.3, the image signal   V1  ⁢      xe2x80x83    ⁢  o  ⁢      xe2x80x83    ⁢  f  ⁢      xe2x80x83    ⁢      3    10  
is reflected to the output image Out1, while the image signal             V2      ⁢              xe2x80x83            ⁢      o      ⁢              xe2x80x83            ⁢      f      ⁢              xe2x80x83            ⁢      1        -          3      10        =      7    10  
is reflected to the output image Out1.
Accordingly, the image signals V1 and V2 are displayed on the screen at a transparency ratio reflected by the calculation.
The above OSD technology is implemented in hardware as shown in FIG. 1. Referring to FIG. 1, a related art OSD apparatus includes a first combining unit 3 for combining a predetermined blend coefficient xcex1 with a predetermined image signal V1, a subtractor 1 for outputting a value obtained by subtracting the blend coefficient xcex1 from 1, a second combining unit 2 for combining a value output from the subtractor 1 with another image signal V2, an adder 4 for adding a value of the first combining unit 3 to a value of the second combining unit 2, and a rounding/limiting unit 5 for receiving a signal output from the adder 4 and controlling its final output signal.
The rounding/limiting unit 5 forcibly converts an input value exceeding 255 to a value of 255 in case of 8-bit image (the contrast range of 0 to 255), and also forcibly converts an input value of less than 0 to 0. As a result, the final output signal does not depart from the contrast range.
The aforementioned related art for OSD technology has an advantage in that it can be simply implemented in hardware when displaying two different images using the blending method. However, the related art has several disadvantages. For example, some resulting images may be difficult to identify in a specific image region. This is due to the fact that it applies the same blend coefficient xcex1 to all of the image regions, regardless of the basis that cognition of a human being on an image is varied depending on the characteristics of the image regions. Because of the above reason, it may also cause a phenomenon where respective input images appear to be blended at different ratios depending on the regions.
Accordingly, the present invention is directed to an OSD apparatus and method for displaying on-screen images that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
To solve the above problems, an object of the present invention is to provide an OSD apparatus and method for displaying output images in which all input images are reflected. All input images would be reflected upon resultant images by identifying a Human Visual System (HVS) in an image region displayed on a screen and a peripheral region.
To achieve the above object, an apparatus for displaying an OSD according to the present invention includes a region search device for obtaining characteristic elements of a Human Visual System (HVS). The device searches the respective regions of an image and calculates either a blend coefficient value based on the following: HVS or a parameter which changes an input image, xcex1 controller for designating a blend coefficient value xcex1 using the blend coefficient xcex1 or parameter calculated by the region search device.
According to one embodiment of the present invention, an OSD apparatus for displaying an image using first and second video input signals and a blend coefficient value, comprises a region search device for generating an output signal, wherein the output signal is responsive to Human Visual System (HVS) characteristic elements and the first and second video input signals; an xcex1 controller responsive to the blend coefficient value and the output signal from the region search device, wherein the xcex1 controller outputs a controlled blend coefficient; a first combining unit for combining the controlled blend coefficient with the first video input signal; a subtractor for outputting a difference between a predetermined value, for example 1, and the controlled blend coefficient; a second combining unit for combining an output from the subtractor with the second video input signal; an adder for adding output values of the first combining unit and the second combining unit; and a rounding/limiting unit for controlling an output from the adder within a predetermined contrast range.
According to one aspect of the present invention, the contrasts of the first and second video input signals are used as one of the HVS characteristic elements. Preferably, the contrasts of the first and second video input signal are obtained by selectively considering contrast of at least one of horizontal, vertical, and diagonal directions. Alternatively, at least one of frequency, background brightness and contrast is selectively used as the HVS characteristic elements.
According to another aspect of the present invention, the contrast is obtained by using a Y component when the first and second video input images are YUV images.
According to another aspect of the present invention, the controlled blend coefficient is determined by using contrasts of the first and second video input signals, the controlled blend coefficient being the same as the blend coefficient when the contrasts of the first and the second video input signals are low.
According to another aspect of the present invention, the controlled blend coefficient is determined by using contrasts of the first and the second video input signals, the controlled blend coefficient being adjusted from the blend coefficient when a contrast difference between the first and the second video input signals is high. Preferably, the controlled blend coefficient is adjusted by the contrast difference divided by 2n, wherein n is a number of bits representing each one of the first and the second video input signals.
According to another aspect of the present invention, the controlled blend coefficient is determined by using contrasts of the first and the second video input signals, the controlled blend coefficient being adjusted from the blend coefficient when the contrasts of the first and the second video input signals are high. Preferably, the controlled blend coefficient is adjusted by the contrast difference divided by 2n, wherein n is a number of bits representing each one of the first and the second video input signals.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide a further explanation of the invention as claimed.